Fan blade tips

ABSTRACT

Fans having blade tips with downwardly extending airfoil surfaces are disclosed herein. In one embodiment, for example, a high volume low speed ceiling fan includes a plurality of blades, each having an anhedral or downward sloping tip portion. The blade tips can also include an aft swept portion that extends between the main airfoil portion of the fan blade and the anhedral tip portion.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Application No. 61/416,680, filed Nov. 23, 2010, and entitled “FAN BLADE TIPS,” which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The following disclosure relates generally to fan blades and, more particularly, to high efficiency fan blade tips.

BACKGROUND

Multi-blade, high velocity low speed (HVLS) cooling fans are often used in warehouses, loading docks, and other large structures to provide a comfortable work environment and/or to maintain suitable temperatures for product storage. Such fans are typically hung from the ceiling, and can include a plurality of blades extending outwardly from a central, motor-driven hub.

Conventional ceiling fan blades are generally flat and have constant cross-sections from root to tip. Others can include upwardly-angled airfoil extensions on the tips, or flat plates that simply cap off the tips as taught in, for example, U.S. patent application Ser. No. 12/038,873, and U.S. Pat. Nos. 7,252,478, 7,284,960 and 7,654,798 (each of these patents and applications is incorporated herein by reference). While these tip devices may improve the aerodynamic characteristics of conventional fan blades, further reductions in aerodynamic drag, power consumption, and acoustic signature would be beneficial.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric top view of a fan having a plurality of blades with blade tips configured in accordance with an embodiment of the disclosure.

FIGS. 2A-2C are corresponding top, front, and end views, respectively, of a portion of the fan blade of FIG. 1 illustrating various aspects of the blade tip in more detail.

FIGS. 3A-3C are corresponding top, front, and end views, respectively, of a portion of a fan blade having a blade tip configured in accordance with another embodiment of the disclosure.

FIGS. 4A-4C are corresponding top, front, and end views, respectively, of a portion of a fan blade having a blade tip configured in accordance with a further embodiment of the disclosure.

DETAILED DESCRIPTION

The present disclosure describes various embodiments of fan blade tips for use with various types of cooling fans. In one embodiment, a ceiling fan configured in accordance with the present disclosure can include a plurality of blades having tips with an anhedral portion. More specifically, the blade tips can include a winglet or similar airfoil surface that slopes downwardly and away from the main airfoil portion of the fan blade. In another embodiment, the blade tips can include an aft swept portion that lies in the same plane as the main airfoil portion, and an anhedral portion that extends downwardly from the aft swept portion. The anhedral portion can also be swept aft and can include a tapered profile. As discussed in greater detail below, providing fan blades with downwardly sloping (i.e., anhedral) winglets or tip portions with or without an aft swept horizontal portion can reduce air dynamic drag on the fan blades during operation, thereby improving efficiency, reducing power requirements, and reducing the acoustic signature of the fan.

Certain details are set forth in the following description and in FIGS. 1-4C to provide a thorough understanding of various embodiments of the disclosure. Other details describing well-known structures and systems often associated with fans, fan blades, HVLS cooling fans, etc. have not been set forth in the following disclosure to avoid unnecessarily obscuring the description of the various embodiments of the disclosure.

Many of the details, dimensions, angles and other features shown in the Figures are merely illustrative of particular embodiments of the disclosure. Accordingly, other embodiments can have other details, dimensions, angles and features without departing from the spirit or scope of the present invention. In addition, those of ordinary skill in the art will appreciate that further embodiments of the invention can be practiced without several of the details described below.

In the Figures, identical reference numbers identify identical, or at least generally similar, elements. To facilitate the discussion of any particular element, the most significant digit or digits of any reference number refers to the Figure in which that element is first introduced. For example, element 110 is first introduced and discussed with reference to FIG. 1.

FIG. 1 is a top isometric view of a cooling fan 100 having downwardly-extending blade tip devices configured in accordance with an embodiment of the disclosure. In the illustrated embodiment, the fan 100 is a high velocity low speed (HVLS) cooling fan having a plurality of blades 110 (identified individually as blades 110 a-110 f) extending outwardly (e.g., radially outward) from a central hub 112. Such fans can have outer diameters (as defined by the blade tips) greater than, for example, 4 feet, such as from about 4 feet to about 28 feet in some embodiments, and from about 6 feet to about 24 feet in other embodiments. The central hub 112 is operably coupled to a drive motor 102 (e.g., an electric motor) by means of a gearbox 114. The motor and gearbox assembly can be carried by a support frame 104 that is pivotally coupled to a mounting plate 106 by means of a universal joint 108. The mounting plate 106 can be fastened to a ceiling or other elevated structure using bolts or other suitable fasteners known in the art. The fan drive and mounting components described above can be of conventional design and construction and, accordingly, require no further description herein. Moreover, the fan 100 is merely illustrative of one type of fan that can utilize the novel blade tip configurations and devices disclosed herein. In other embodiments, the fan blade tips described herein can be used with other types of fans having, for example, other types of blades, drive systems, and/or mounting systems, without departing from the spirit or scope of the present disclosure.

In the illustrated embodiment, each of the fan blades 110 includes a main airfoil 120 having an inboard end portion 116 fixedly attached to the central hub 112, and an outboard end portion 118 fixedly attached to a blade tip 122. In one aspect of this embodiment, the blade tip 122 includes an aft swept portion 124 and a downwardly sloping “anhedral” portion 126. Without wishing to be bound by theory, the blade tips 122 are believed to produce tip vortices with improved drag characteristics as the fan blades 110 rotate through the air in the direction of arrow R. As is known, wingtip or blade tip vortices are spirals of circulating air which are shed from the tips as the blades deflect the air downwardly in the direction of arrow D. As the vortex curls over the tip of a conventional fan blade, it reduces lift near the tip of the fan blade and creates turbulent air through which the trailing blade must move. Each of these factors increases the drag and reduces the efficiency of the fan. It is believed that by providing the anhedral portion 126 at a downward slope, the vortex is shed from the tip 122 at a vertical location that is below the waterline of the main airfoil 120. This tends to direct the vortex downward and away from the trailing blade. It is also believed that by angling the swept portion 124 aft, the vortex curls over the blade tip 122 aft of the trailing edge of the main airfoil 120, thereby reducing the turbulent airflow striking the upper surface of the main airfoil 120. It is further believed that tapering the profile of the anhedral portion 126 can reduce turbulence generated by the blade tip 122. All of the foregoing factors contribute to a cooling fan blade that generates less aerodynamic drag, thereby improving efficiency and reducing power requirements for a given output, as well as reducing the acoustic signature of the fan.

FIGS. 2A-2C are corresponding top, front, and end views, respectively, of the outboard portion of the fan blade 110 described above with reference to FIG. 1. In FIGS. 2A-2C, the blade 110 rotates in the direction of arrow R. Down is designated by the arrow D, which is defined by the direction in which the fan blades 110 move air during normal operation (i.e., rotation in direction R), and up is designated by arrow U. In the illustrated embodiment, the main airfoil 120 can have an elongate rectangular planform with a conventional airfoil cross-section. As is known, in some embodiments the main airfoil 120 can have an angle of attack or upward inclination to deflect the air downward in direction D during operation. The swept portion 124 and the anhedral portion 126 can have complimentary airfoil cross-sections. As shown in FIG. 2B, the swept portion 124 of the blade tip 122 lies in the same plane as the main airfoil 120, and is swept aft relative to the direction of rotation R. In the illustrated embodiment, the swept portion 124 has an inboard chord C₁ that is at least approximately equal to an outboard chord C₂. That is, in the illustrated embodiment the swept portion 124 can have a generally constant chord. The anhedral portion 126, however, can taper outwardly such that a tip chord C₃ is less than the swept portion chord C₂. In other embodiments, however, the main airfoil 120, the swept portion 124, and/or the anhedral portion 126 can have other shapes, sizes and angles.

As shown in FIG. 2B, the thickness of the anhedral portion 126 also decreases as it moves outboard. More specifically, the root of the anhedral portion 126 has a first thickness t₁ that is greater than a corresponding tip thickness t₂. As mentioned above, it is believed that reducing the chord thickness or profile of the anhedral portion 126 in this way provides improved airflow characteristics when compared with a blade tip having a constant thickness.

The present disclosure is not limited to the particular embodiment of fan blade tip described above with reference to FIGS. 2A-2C. FIGS. 3A-3C, for example, are corresponding top, front, and end views, respectively, of a portion of a fan blade 310 having a blade tip 322 configured in accordance with another embodiment of the disclosure. In this embodiment, the aft swept portion 324 tapers slightly in chord length from the inboard chord C₁ to a narrower outboard chord C₄. Moreover, in this embodiment the blade tip 322 includes a downwardly-angled anhedral portion 334 having a curved leading edge 332 and a curved trailing edge 334. In the illustrated embodiment, the curved leading edge 332 forms a convex parabolic curve and the curved trailing edge 334 forms a concave parabolic curve. The leading edge 332 and the trailing edge 334 intersect at tip point 336. As illustrated by FIGS. 2A-3C, the shapes, angles, tapers, and other dimensional aspects of the blade tips described herein can be adjusted to suit a particular blade profile, speed, performance characteristic, etc. Accordingly, the present disclosure is not limited to the specific shapes, profiles, thicknesses, and/or other geometric aspects of the blade tips described above.

Although the blade tips 222 and 322 described above with reference to FIGS. 2A-3C include an aft swept portion 124, 324. In other embodiments, other fan blade tips configured in accordance with the present disclosure can omit the aft swept portions 124, 324. FIGS. 4A-4C, for example, are corresponding top, front, and end views, respectively, of a fan blade 410 having a blade tip 422 with an anhedral portion 426 fixedly attached directly to an outboard end 418 of a main airfoil 420. While such a configuration may not provide all of the advantages of the blade tips 122 and 322 described above, the blade tip 422 may still provide advantages over a conventional fan blade tip and may be more cost effective to manufacture and install than the blade tips 122 and 322. Although the anhedral portion 426 includes curved leading and trailing edges (e.g., having parabolic curves), it will be understood that in other embodiments the anhedral portion 426 and suitable variations thereof can have straight leading and/or trailing edges, and/or can include a round tip or a squared off tip such as the anhedral portion 126 described above with reference to FIGS. 2A-2C.

The various embodiments of fan blades and blade tips described above can be manufactured using any number of different materials and methods known in the art. For example, all or a portion of the fan blades can be formed from plastic, such as injection molded plastic, composites, metal, and/or other suitable materials. Moreover, in some embodiments the main airfoil (e.g., the main airfoil 120, 320, or 420) and the blade tip (e.g., the blade tip 122, 322, or 422) can be integrally formed as single unit. In another embodiment, the blade tip can be manufactured as a separate unit that is retrofit to existing fan blades to increase efficiency and enhance performance.

From the foregoing, it will be appreciated that specific embodiments of the invention have been described herein for purposes of illustration, but that various modifications may be made without deviating from the spirit and scope of the various embodiments of the invention. Further, while various advantages associated with certain embodiments of the invention have been described above in the context of those embodiments, other embodiments may also exhibit such advantages, and not all embodiments need necessarily exhibit such advantages to fall within the scope of the invention. Accordingly, the invention is not limited, except as by the appended claims. 

1. A ceiling fan comprising: a central hub configured to be suspended from a ceiling of a building; and a plurality of blades extending outwardly from the central hub, wherein each blade includes: a main airfoil having an inboard end portion fixedly attached to the central hub and an outboard end portion spaced apart from the central hub; and a tip portion attached toward the outboard end portion of the main airfoil and extending downwardly relative to the main airfoil portion.
 2. The ceiling fan of claim 1 wherein the plurality of blades define a fan outer diameter of from about 6 feet to about 24 feet.
 3. The ceiling fan of claim 1 wherein the main airfoils extend horizontally outward from the hub.
 4. The ceiling fan of claim 1 wherein each blade further includes an aft swept portion attached to the outboard end portion of the main airfoil between the outboard end portion and the tip portion, and wherein the tip portion extends downwardly relative to the aft swept portion.
 5. The ceiling fan of claim 1 wherein each blade further includes an aft swept portion attached to the outboard end portion of the main airfoil between the outboard end portion and the tip portion, wherein the main airfoil and the aft swept portion of each blade lie in a horizontal plane, and wherein the tip portion extends downwardly relative to the aft swept portion.
 6. A fan comprising: a motor driven central hub; and a plurality of blades extending outwardly from the central hub fan, wherein the plurality of blades are configured to move air in a direction D when rotating in a direction R during normal operation, wherein each blade includes: a main airfoil having an inboard end portion fixedly attached to the central hub and an outboard end portion spaced apart from the central hub; and a tip having: an aft swept portion; and an anhedral portion, wherein the aft swept portion has an inboard chord attached to the outboard end portion of the main airfoil and an outboard chord attached to anhedral portion, and wherein the anhedral portion extends away from the main airfoil in direction D.
 7. The fan of claim 6 wherein the inboard end portion and the outboard end portion of the main airfoil lie in a common plane, and wherein the anhedral portion is positioned at an angle relative to the plane.
 8. The fan of claim 6 wherein the main airfoil and the aft swept portion lie in a common plane, and wherein the anhedral portion is positioned at an angle relative to the plane.
 9. The fan of claim 6 wherein the aft swept portion extends away from the main airfoil opposite to the direction R.
 10. The fan of claim 6 wherein the anhedral portion extends away from the aft swept portion opposite to the direction R.
 11. The fan of claim 6 wherein the main airfoil and the aft swept portion lie in a common plane, wherein the anhedral portion is positioned at an angle relative to the plane, wherein the aft swept portion extends away from the main airfoil opposite to the direction R, and wherein the anhedral portion extends away from the aft swept portion opposite to the direction R.
 12. The ceiling fan of claim 6 wherein the main airfoil and the aft swept portion have complimentary airfoil cross sections and lie in a common horizontal plane, and wherein the anhedral portion has a first chord thickness where it attaches to the aft swept portion and a second chord thickness a distal tip, and wherein the first chord thickness is greater than the second chord thickness.
 13. The ceiling fan of claim 6 wherein the main airfoil has a rectangular planform and the aft swept portion and the anhedral portion taper outwardly.
 14. The ceiling fan of claim 6 wherein the anhedral has a curved leading edge and a curved trailing edge.
 15. The ceiling fan of claim 6 wherein the anhedral portion has a curved leading edge that forms a convex parabolic curve and a curved trailing edge that forms a concave parabolic curve.
 16. A fan comprising: a central hub; means for rotating the central hub; means for coupling the means for rotating to a ceiling or other elevated structure in a building; and a plurality of blades extending outwardly from the central hub, wherein each blade includes: a main airfoil having an inboard end portion fixedly attached to the central hub and an outboard end portion spaced apart from the central hub; and a tip portion attached toward the outboard end portion of the main airfoil and extending downwardly relative to the main airfoil portion.
 17. The fan of claim 16 wherein the plurality of blades define a fan outer diameter of from about 6 feet to about 24 feet.
 18. The fan of claim 18 wherein each blade further includes an aft swept portion attached to the outboard end portion of the main airfoil between the outboard end portion and the tip portion, and wherein the tip portion extends downwardly relative to the aft swept portion.
 19. The fan of claim 18 wherein each blade further includes an aft swept portion attached to the outboard end portion of the main airfoil between the outboard end portion and the tip portion, wherein the main airfoil and the aft swept portion of each blade lie in a horizontal plane, and wherein the tip portion extends downwardly relative to the aft swept portion. 